Television transmitting or receiving system



2 Sheets-Sheet 1 c. L. FAUDE'LL 1 Filed March '7, 1940 INVENTOR c. L. 1-74 UDELL IA ORNEY TELEVISION TRANSMITTING OR RECEIVING SYSTEM Um. I, 11942.

we, L H942. c. L. FAUDELL 3 TELEVISION TRANSMITTING QR RECEIVING SYSTEM 2 Sheets-Sheet 2 Filed March '7, l9 40 INVENTOR c. L. FA .uosu.

ATTORNEY Patented cc. 1, rate rnLnvrsroN TRANS r 1 1:!" G SYSTE Charles Leslie Faudell, Stoke Poges, England, as-

signor to Electric & Musical Industries Limited, Hayes, Middlesex, En

Great Britain gland, a company of Application March 7, 1940, Serial No. 322,678 In Great Britain March 7, 1939 4 Claims.

The present invention relates to a television transmitter or receiver of the kind employing a cathode ray tube in which the beam of cathode rays is subjected to periodic deflections so that the beam is caused to scan continuously the screen of the cathode ray tube.

In a television transmitter or receiver of the above kind, during the line and frame return periods the cathode ray beam is usually suppressed so as to aiford no visible trace on the screen during these periods.

It is the object of the present invention to provide improved means for suppressing the beam during the frame and/or line return periods the invention being applicable either totelevision transmitters or to receivers of the above kind.

According to the present invention a television receiver or transmitter of the above kind is provided having a thermionic valve relaxation oscillator for generating potentials of a substantially saw tooth waveform for deflecting the oathode ray beam, wherein said valve is arranged to be rendered conducting periodically for generating the short flanks of the saw tooth waveform and wherein during the conducting period said valve is arranged to generate a bias potential which is applied to said cathode ray tube to suppress the beam during the return periods of the beam.

Reference will now be made to the accompanying drawings which comprise Figures 1 to 5, Figures 1 to 4 illustrating circuits embodying the present invention by way of example, and Fig. 5 being an explanatory diagram.

In Figure 1 the present invention is illustrated applied to a known blocking oscillator which is employed to generate saw-tooth potentials for application to the frame deflecting means of a cathode ray tube. When the valve I is non-conducting, the condenser C2 is steadily charged from the source of supply, indicated by the conventional positive and negative signs, through the resistance R2 to generate the long flank of the saw tooth waveform potentials. The control grid 5 and screen grid 6 of the valve I are coupled together by the windings l and 8 of a transformer, the grid 5 being connected to the cathode t by a circuit which includes a condenser C1 and grid leak resistance R1. ing rendered conducting, for example by the application of a synchronising pulse, the valve is rendered conductin and causes the rapid discharge of the condenser C2, thus generating the short flank of the saw-tooth and consequently the frame return deflection of the cathode ray beam, and at the same time a pulse of current flows in the coil 8. The valve remains conducting until, due to the flow of grid current to the grid 5 as a result of the coupling between coils I l and 8, the condenser C1 becomes charged to On the valve I besuch a value of negative potential that current ceases to flow from the cathode t to the anode 2. In accordance with the present invention when the valve I is rendered conducting it serves to generate a bias potential which is applied to the cathode II of the cathode ray tube to extinguish the beam during the frame return period when the short flank of the saw tooth wave potentials in being produced.

A coil 9 is coupled with the coil 8 and connected with the coil 9 is a resistance III. A potential is thus set up across the resistance III on the occurrence of each frame-return deflection of the cathode ray beam. The resistance I0 is suitably tapped and connected to the cathode II of the cathode ray tube 3, the values of the components 9 and I ll of the circuit being adjusted so that the potential applied to the cathode II is of sufficient value, and of the correct phase, to cause the suppression of the cathode ray beam on a frame return periodic deflecting voltage being applied to the scanning means. If the resistance I0 is connected to the modulating electrode I2 of the cathode ray tube 3, the potential applied to electrode I2 would require to b 180 degrees out of phase with the potential utilised when connection is made to the cathode I I.

The circuit illustrated in Figure 2 is substantially the same as that of Figure 1, but here the blocking potential applied to he cathode I I of 'the cathode ray tube is derived from a. tapping on the coil I which is connected in the circuit of the grid 5 of the valve I. The cathode II is connected to the tapping on the coil I by way of a. condenser I3 and resistance It, the condenser I3 and resistance I4 being connected in parallel between the tapping point and one end of the coil 1, the potential produced at the junction of condenser I3 and resistance It being applied to the cathode II. The condenser I3 and resistance It produce an increase of the duration of the pulses of current and thus the period for which the blocking potential applied to the cathode II is efiective may be adjusted, ensuring that it is effective at least for the period during which the beam is defiected to its required position.

The circuit illustrated in Figure 3 is also substantially the same as Figure 1, but the cathode II of the cathode ray tube is connected to the end of the coil I, which coil 1 is connected by a resistance It and condenser I'l, arranged in parallel, to the cathode of valve l instead of directly to the cathode of valve I. A positive pulse of current is formed across the resistance I6 when the valve I is rendered conducting and this pulse decays through the condenser H. The amplitude of the pulse may be adjusted by variation of the resistance I6, its duration adjusted by variation of the capacity of the condenser II.

The major part of the circuit illustrated in site end of the coil 1 to the cathode l of the valve I ,-the condenser C being shunted by the resistance R1. A condenser C: is connected from the junction of resistance R1 and condenser C1 to the cathode of a diode [8, the cathode of the diode being connected to, the cathode of valve t by a variable resistance R3, whilst the anode of diode I8 is connected to the cathode of valve 4 by a resistance R4, the voltages appearing across R4 being applied to the grid i2 of the cathode ray tube 3.

An exponential sawtooth potential of considerable amplitude, of the order of 150 volts, is developed across the cathode t and the junction of the resistance R1 and condenser C1, the waveform of this potential being left illustrated in the left-hand portion of Fig. 5. The diode l8 acts as an amplitude selector, becoming conductive only when the potential at the junction of resistance R1 and C1 is below a suitable value indicated by the line OX in Fig. 5; when the potential of the junction of R1 and C1 exceeds this value the diode I8 is rendered non-conducting. Thus only the negative tips of the potential waveform illustrated in the right-hand portion of Fig. 5, are efiective to apply a voltage to the cathode ray tube 3. The voltages then appearing across R4 being negative, the grid [2 of cathode ray tube 3 causes substantial suppression of the cathode ray beam for the period that the sawtooth potential lies below the line OX.

The amplitude of the sawtooth potential may be varied, by altering the value of resistance R or resistance R4, so as to adjust the bias applied to the diode l8, and since the rise in potential is of an exponential form, adjusting the bias applied to the diode l8 also serves to adjust the period for which the cathode ray beam of tube 3 is substantially suppressed. The time constant produced by R3 and Ca must be appreciably greater than that of R1 and C1 so that the waveform of the exponential sawtooth is not substantially afi'ected with variations in R3.

The blocking potential obtained from a coil such as I or 8 or from a resistance connected with one of these coils may be applied to any convenient electrode of the cathode ray tube.

Also, although embodiments of the present invention have been described in connection with a valve providing frame frequency deflections the present invention may also be employed in connection with the linefrequency deflections.

As herein-before described the valve l serves electrostatic energy storage means being connected substantially in parallel with the anodecathode space discharge path of said tube, a time constant circuit connected in the control electrode cathode path of said tube whereby a pulse is developed therein during the discharge of the energy stored in said electrostatic energy storage means, and a connection between the resistive member of said time constant circuit and an element of said cathode ray tube whereby at least a portion of the pulse developed in the control electrode-cathode circuit of said tube is impressed onto an element of said cathode ray tube to suppress the beam.

2. A cathode ray beam suppression system .for suppressing a cathode ray beam developed within afcathode ray tube comprising a thermionic tube having anode, cathode and at least one control electrode, electrostatic energy storage means connected substantially in parallel with the anode-cathode space discharge path of said thermionic tube, means for storing energy in said electrostatic energy storage means during the time whensaid tube is impervious to electron flow, a time constant circuit connected in the control electrode-cathode path of said tube in which energy is stored during the discharging of the energy in said electrostatic energy storage means through the space discharge path of said thermionic tube, uni-directional conducting means, and means for impressing the energy stored in said time constant circuit onto said uni-directional conducting means, and means for impressing the output of said uni-directional con ducting means onto an electrode of the cathode ray tube in which said cathode ray beam is developed for suppressing the said beam.

3. Apparatus for suppressing a cathode ray beam developed within a cathode ray tube comprising electrostatic energy storage means, means for storing energy in said electrostatic energy storage means, a discharge path for said electro static energy storage means comprising the space discharge path of a thermionic tube, said tube having anode, cathode, and at least one control electrode, the anode-cathode space discharge path of said thermionic tube being connected substantially in parallel with said electrostatic energy storage means, a time constant circuit connected in the control electrode-cathode path of said thermionic tube, means for feeding back to a control electrode-cathode path of said tube a portion of the energy developed in the anodecathode path of said tube during the discharge of said electrostatic energy storage means, and means for impressing at least a portion of said fed back energy onto an element of the cathode ray tube to suppress the cathode ray beam.

4. Apparatus for suppressing a cathode ray beam developed within a cathode ray tube comprising electrostatic energy storage means, means for storing energy in said electrostatic energy storage means, a discharge path for said electrostatic energy storage means comprising the space discharge path of a thermionic tube, said tube having anode, cathode, and at least one control electrode, the anode-cathode space discharge path of said thermionic tube being connected substantially in parallel with said electrostatic energy storage means,'means for feeding back at least a portion of the energy in the anodecathode circuit of said thermionic tube during the discharge of said electrostatic energy storage means to a control electrode-cathode path of said thermionic tube, and means coupled to said control electrode-cathode path of said thermionic tube and to an element of said cathode ray tube for impressing a portion of the fed back energy onto the cathode ray tube.

CHARLES LESLIE FAUDELL. 

